Analytical Modeling of Solid Material Ignition Under a Radiant Heat Flux Coming From a Spreading Fire Front

2014 ◽  
Vol 6 (4) ◽  
Author(s):  
A. Lamorlette
Keyword(s):  
Heat Flux ◽  
Ignition Time ◽  
Thermal Inertia ◽  
Solid Material ◽  
Radiant Heat ◽  
Heat Fluxes ◽  
Polynomial Coefficients ◽  
Rate Of Spread ◽  
Fire Front ◽  
Ignition Times

This study aims at characterizing ignition of solid targets exposed to spreading fire fronts. In order to model radiant heat fluxes on targets in a realistic way, polynomial heat fluxes are chosen. Analytical solutions for the solid surface temperature evolution regarding different time-varying heat fluxes are discussed for high thermal inertia solids using a mathematical formalism, which allows for the methodology to be extended to the case of low thermal inertia. This formulation also allows calculation of ignition times for more realistic time-dependent fluxes than previous studies on the topic, providing a more general solution to the problem of solid material ignition. Polynomial coefficients are then obtained fitting heat flux coming from absorbing–emitting flames. A characterization of solid material ignition times regarding fire front rate of spread (ROS) is finally performed, showing the need to accurately model heat flux variations in ignition time calculations.

scholarly journals Experimental Study of Oriented Strand Board Ignition by Radiant Heat Fluxes

Polymers ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 709
Author(s):  
Ivana Tureková ◽  
Iveta Marková ◽  
Martina Ivanovičová ◽  
Jozef Harangózo
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Elevated Temperatures ◽  
Oriented Strand Board ◽  
Ignition Time ◽  
Radiant Heat ◽  
Heat Fluxes ◽  
Composite Panel ◽  
Substantial Part ◽  
Ignition Times

Wood and composite panel materials represent a substantial part of the fuel in many building fires. The ability of materials to ignite when heated at elevated temperatures depends on many factors, such as the thermal properties of materials, the ignition temperature, critical heat flux and the environment. Oriented strand board (OSB) without any surface treatment in thicknesses of 12, 15 and 18 mm were used as experimental samples. The samples were gradually exposed to a heat flux of 43 to 50 kW.m−2, with an increase of 1 kW.m−2. At heat fluxes of 49 kW.m−2 and 50 kW.m−2, the ignition times are similar in all OSB thicknesses, in contrast to the ignition times at lower heat fluxes. The influence of the selected factors (thickness and distance from the heat source) was analysed based on the experimentally obtained data of ignition time and weight loss. The experimentally determined value of the heat flux density was 43 kW.m−2, which represented the critical heat flux. The results show a statistically significant effect of OSB thickness on ignition time.

Development of a pyrolysis model for oriented strand board: Part II—Thermal transport parameterization and bench-scale validation

2021 ◽  
pp. 073490412110366
Author(s):  
Junhui Gong ◽  
Hongen Zhou ◽  
Hong Zhu ◽  
Conor G McCoy ◽  
Stanislav I Stoliarov
Keyword(s):  
Heat Flux ◽  
Mass Loss ◽  
Loss Rate ◽  
Oriented Strand Board ◽  
Mass Loss Rate ◽  
Radiant Heat ◽  
Heat Fluxes ◽  
Controlled Atmosphere ◽  
Radiant Heat Flux ◽  
Pyrolysis Model

Oriented strand board is a widely used construction material responsible for a substantial portion of the fire load of many buildings. To accurately model oriented strand board fire response, kinetics and thermodynamics of its thermal decomposition and combustion were carefully characterized using milligram-scale testing in part I of this study. In the current work, Controlled Atmosphere Pyrolysis Apparatus II tests were performed on representative gram-sized oriented strand board samples at a range of radiant heat fluxes. An automated inverse analysis of the sample temperature data obtained in these tests was employed to determine the thermal conductivities of the undecomposed oriented strand board and condensed-phase products of its decomposition. A complete pyrolysis model was formulated for this material and used to predict the mass loss rates measured in the Controlled Atmosphere Pyrolysis Apparatus II experiments. These mass loss rate profiles were predicted well with the exception of the second mass loss rate peak observed at 65 kW m−2 of radiant heat flux, which was underpredicted. To further validate the model, cone calorimeter tests were performed on oriented strand board at 25 and 50 kW m−2 of radiant heat flux. The results of these tests, including both mass loss rate and heat release rate profiles, were predicted reasonably well by the model.

scholarly journals The Roseville Bomb Disaster Simulated Train Braking System Tests and Boxcar Wood Floor Ignition Experiments

1991 ◽  
Vol 113 (1) ◽  
pp. 91-99
Author(s):  
B. Ross ◽  
P. G. Parikh
Keyword(s):  
Heat Flux ◽  
Cast Iron ◽  
Ignition Time ◽  
Thermal Response ◽  
Radiant Heat ◽  
Full Scale ◽  
Test Facility ◽  
Shield Effectiveness ◽  
Wood Floor ◽  
Wood Surfaces

A massive chain of property damaging explosions involving an ammunition train occurred at the railroad yard, Roseville, California. The train had pulled into the yard after a night trip of some 100 miles across Donner Summit and down the extended Norden-Roseville grade. Physical evidence confirmed that first explosions were centered at a DODX type boxcar loaded with 250 lb. bombs. Further, bomb cook-off detonation tests established that the triggering bomb blast was not a result of shock loads but rather derived from an engulfing fire initiated in the boxcar wood plank floor under influence of extended heavy braking action on the mountain grade. It was also suspected that high friction composition brake shoes were fitted on the car as replacements for cast iron shoes but the brake mechanical linkage lever ratios had not been modified as required. Results of a comprehensive research program are presented within context of the explosion event, and include analytical computer simulation of train descent profiles on mountain grades through full scale dynamometer tests with actual rail wheels and ultimately more scientific scaled wood floor ignition experiments in the laboratory. The thermal response of a simulated DODX boxcar wood floor was studied through experiments, full scale at a rail wheel dynamometer test facility, and in the laboratory. Certain input data for the wood floor ignition test program were measured on an actual boxcar joined with a freight train consist in transit down the Norden-Roseville grade. Two series of scaled wood ignition experiments were conducted on simulated DODX boxcar floors. Objectives of these tests were to determine: Influence of a cooling air stream on the ignition behavior of radiantly heated wood surfaces, and effectiveness of DODX (stand-off) and AAR (flush) type spark shields in preventing ignition of wood surfaces under radiant heating. It was found that for radiant heat flux levels representative of high friction composition shoes under severe train braking conditions, low speed airflow (wind) exerts a dramatic influence on the wood ignition time. For example, average ignition time for a simulated boxcar floor at a heat flux level of 0.4 cal/cm2sec was determined to be 15.6 min. with a 5 mph wind as compared to 3.6 min. with no wind. In the spark shield effectiveness tests, conducted at heat flux levels representative of cast iron shoes under severe braking conditions, the DODX (stand-off) type spark shield failed to prevent spontaneous flaming ignition of a wood surface directly above it. Under identical conditions, no flaming ignition was encountered with the AAR (flush) type spark shield.

Modeling Exposures of a Nylon-Cotton Fabric to High Radiant Heat Flux

2016 ◽  
Vol 11 (3) ◽  
pp. 155892501601100
Author(s):  
Thomas Godfrey ◽  
Margaret Auerbach ◽  
Gary Proulx ◽  
Pearl Yip ◽  
Michael Grady
Keyword(s):  
Heat Flux ◽  
Cone Calorimeter ◽  
Burn Injury ◽  
Thermal Protection ◽  
Transient Heat Conduction ◽  
Radiant Heat ◽  
Heat Fluxes ◽  
Direct Result ◽  
Face Modeling ◽  
Flaming Combustion

American soldiers and marines involved in the recent conflicts in Iraq and Afghanistan have suffered increased incidence of burn injury, often as a direct result of exposure to improvised explosive devices. In this work, a one dimensional numerical pyrolysis model for transient heat conduction, incorporating material transformations described by chemical kinetics, is used to investigate the response of the standard 230 g/m2 Army Combat Uniform (ACU) fabric to high radiant heat fluxes in short duration thermal protection tests and long duration cone calorimeter tests. Thermal protection tests are performed using a Thermal Barrier Test Apparatus–an automated device, incorporating a closed-loop controlled IR radiant heat source, automated water cooled shutter, a fabric sample holder, an adjustable stage with a water cooled Schmidt-Boelter heat flux gauge and a PC based data acquisition system. Cone calorimeter tests are performed on fabric specimens at an exposure heat flux of 25 kW/m2. In thermal protection tests involving exposures of 90 kW/m2 for five seconds and 77 kW/m2 for four seconds, modeling indicated that desorption and evaporation of moisture content has an important effect, but melting of the nylon component and material decomposition had insignificant effects on the heat flux transmitted through the fabric back face. Modeling results for cone testing exhibited good agreement for time to ignition and duration of flaming combustion.

scholarly journals Modelling of the Radiant Heat Flux and Rate of Spread of Wildfire within the Urban Environment

Fire ◽  
2019 ◽  
Vol 2 (1) ◽  
pp. 4 ◽  
Author(s):  
Greg Penney ◽  
Steven Richardson
Keyword(s):  
Heat Flux ◽  
Radiant Heat ◽  
Town Planning ◽  
Radiant Heat Flux ◽  
Urban Context ◽  
Rate Of Spread ◽  
Fire Engineering ◽  
Steady Rate ◽  
Planning And Construction ◽  
Shielding Effects

One approach to increase community resilience to wildfire impacts is the enhancement of residential construction standards in an effort to provide protective shelters for families within their own homes. Current wildfire models reviewed in this study assume fire growth is unrestricted by vegetation fuel bed geometry; the head fire has attained a quasi-steady rate of spread; and the shielding effects of urban development are ignored. As a result, radiant heat flux may be significantly overestimated for small vegetation fires in road reserves, urban parklands, and similar scenarios. This paper proposes two new models to address this issue, and utilises two case studies for comparison against existing approaches. The findings are significant as this is the first study to analyse these factors from a fire engineering perspective, and to demonstrate that the use of landscape scale or siege wildfire models may not be appropriate within the urban context. The development of enhanced wildfire models will have a significant impact on town planning and construction practices in areas prone to wildfires, as well as firefighting suppression efforts when these events occur.

Corrigendum to: Assessing the effect of foliar moisture on the spread rate of crown fires

2013 ◽  
Vol 22 (6) ◽  
pp. 869 ◽  
Author(s):  
Martin E. Alexander ◽  
Miguel G. Cruz
Keyword(s):  
Radiant Heat ◽  
Fire Spread ◽  
Heat Fluxes ◽  
Fuel Moisture ◽  
Conifer Forests ◽  
Spread Rate ◽  
Rate Of Spread ◽  
Crown Fires ◽  
Wide Range ◽  
Live Fuel Moisture

This paper constitutes a digest and critique of the currently available information pertaining to the influence of live fuel or foliar moisture content (FMC) on the spread rate of crown fires in conifer forests and shrublands. We review and discuss the findings from laboratory experiments and field-based fire behaviour studies. Laboratory experimentation with single needles or leaves and small conifer trees has shown an unequivocal effect of FMC on flammability metrics. A much less discernible effect of FMC on crown fire rate of spread was found in the existing set of experimental crown fires carried out in conifer forests and similarly with the far more robust database of experimental fires conducted in shrubland fuel complexes. The high convective and radiant heat fluxes associated with these fires and the lack of appropriate experimental design may have served to mask any effect of FMC or live fuel moisture on the resulting spread rate. Four theoretical functions and one empirical function used to adjust rate of fire spread for the effect of foliar or live fuel moisture were also concurrently examined for their validity over a wide range of FMC conditions with varying outcomes and relevancy. None of these model functions was found suitable for use with respect to dead canopy foliage.

Incorporating vegetation attenuation in radiant heat flux modelling

2015 ◽  
Vol 24 (5) ◽  
pp. 640 ◽  
Author(s):  
Glenn Newnham ◽  
Raphaele Blanchi ◽  
Kimberley Opie ◽  
Justin Leonard ◽  
Anders Siggins
Keyword(s):  
Heat Flux ◽  
Complex Terrain ◽  
Spatial Information ◽  
South Australia ◽  
Radiant Heat ◽  
Separation Distance ◽  
Radiant Heat Flux ◽  
Fire Event ◽  
Fire Front ◽  
Spatially Varying

Models of radiant heat flux (RHF) are critical for understanding wildfire behaviour and the effect a fire may have on homes and people. Various models have been presented in the literature for wildfire RHF, many being based on the Stephan–Boltzmann equation for radiative heat transfer. Most models simplify the fire and receiver interaction by considering a single fuel type at a given separation distance from a receiving point (e.g. on a building requiring protection). However, wildfire is an inherently spatial phenomenon, in that a fire may progress across the landscape towards a building across complex terrain and through spatially varying fuel types. This spatial variation influences the fire behaviour as well as the level of RHF incident on the building. In this study, we present methods for incorporating spatially varying topography and fuels into existing RHF modelling equations. In this way, we achieve a time-dependent profile of the RHF incident on homes, while accounting for attenuation due to fuels and topography that lie between the building and the fire front. The model is applied to the prediction of damage in a fire that occurred in South Australia in 2005. Although only coarse spatial information was available for determining the spatial distribution of fuels, modelled RHF was a significant indicator of house damage. Attenuation due to vegetation between homes and the fire was shown to reduce the modelled RHF exposure of homes. However, this was not shown to increase the significance of predicted house damage in the case of this fire event.

scholarly journals Experimental investigation of the physical mechanisms governing the spread of wildfires

2010 ◽  
Vol 19 (5) ◽  
pp. 570 ◽  
Author(s):  
Frédéric Morandini ◽  
Xavier Silvani
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flame Front ◽  
Fire Regime ◽  
Radiant Heat ◽  
Fire Spread ◽  
Fire Plume ◽  
Physical Mechanisms ◽  
Fire Front ◽  
Observed Behaviour

One of the objectives of the present study is to gain a deeper understanding of the heat transfer mechanisms that control the spread of wildfires. Five experimental fires were conducted in the field across plots of living vegetation. This study focussed on characterising heat transfer ahead of the flame front. The temperature and heat flux were measured at the top of the vegetation as the fire spread. The results showed the existence of two different fire spread regimes that were either dominated by radiation or governed by mixed radiant–convective heat transfer. For plume‐dominated fires, the flow strongly responds to the great buoyancy forces generated by the fire; this guides the fire plume upward. For wind‐driven fires, the flow is governed by inertial forces due to the wind, and the fire plume is greatly tilted towards unburned vegetation. The correlations of the temperature (ahead of the flame front) and wind velocity fluctuations change according to the fire regime. The longitudinal distributions of the radiant heat flux ahead of the fire front are also discussed. The data showed that neither the convective Froude number nor the Nelson convection number – used in the literature to predict fire spread regimes – reflect the observed behaviour of wind‐driven fires.

Pyrolysis and ignition delay time of poly(methyl methacrylate) exposed to ramped heat flux

2018 ◽  
Vol 36 (3) ◽  
pp. 147-163
Author(s):  
Chunjie Zhai ◽  
Fei Peng ◽  
Xiaodong Zhou ◽  
Lizhong Yang
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Methyl Methacrylate ◽  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Ignition Time ◽  
Heat Fluxes ◽  
Critical Surface ◽  
Poly Methyl Methacrylate

Usually, the constant heat flux is used in the previous studies of polymeric pyrolysis. However, the ramped heat flux may be more realistic under a fire condition. For further understandings of polymer pyrolysis in the early stage of fire, the influences of ramped heat flux on pyrolysis of poly(methyl methacrylate) were experimentally and theoretically investigated. Linearly and quadratically ramped heat fluxes were controlled by the output power of a radiative heater. Surface temperature, mass loss rate, and ignition time were experimentally obtained to explore the thermochemical stability of poly(methyl methacrylate) under ramped heat fluxes. A one-dimensional model was used to predict the pyrolysis process, where kinetic parameters were evaluated by a genetic algorithm. Finally, ignition criteria including critical surface temperature and critical mass loss rate were revisited. We observed that the two ignition criteria give similar ignition time when the heat flux increases fast.

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